Seismic performance of masonry cross vaults: learning from historical developments and experimental testing

Considering the seismic behaviour of cultural heritage buildings, an influential role is played by masonry vaults, often representing the most vulnerable part of the construction. Despite their long-lasting history and the damage observation following the Italian earthquakes of the recent past, research in this area is still limited. In this regard, the present thesis is devoted to the study of the seismic behaviour of masonry groin vaults, considered as one of the most diffused vault type in European seismic prone areas in cloisters, palaces and churches. Groin vaults are resulting from the intersection at a right angle of two semi-cylindrical shells on a square bay, and can be addressed as the simplest form of cross vaults, defined as a combination (compound) of curved shells whose thrust converges along the diagonals to isolated abutments. The goal of this work is met via an integration of laboratory tests and numerical analyses. The first part of the thesis reviews the historical developments of the cross vault, the structural methods adopted by the scientific community and the damage evidences after laboratory experiments and post-seismic observation. The subsequent part deals with shaking table tests on a scaled arch built with dry-joint 3D printed voussoirs. The experimental campaign had a twofold purpose. On the one hand it gave insight into the seismic behaviour of masonry arches and, on the other hand, thanks to the tracking motion system employed to record the tests, it provided valuable information to calibrate a three-dimensional numerical model. The physical model was studied using a commercially available FEM software, namely DIANA (from TNO Delft), assuming rigid-infinitely resistant blocks and Coulomb friction interfaces. The nonlinear analyses regarded both the static and dynamic behaviour, shading light on the influence of interface stiffness and damping. The numerical model was subsequently extended to the study of the three-dimensional behaviour of groin vaults. In particular, the analyses focused on the results available in literature following a recent experimental campaign on a 1:5 scaled vault. The model was able to properly catch the maximum strength and the failure mechanism recorded in the quasi-static tests. Analogies between the nonlinear behaviour of the vault and the free-standing rigid block undergoing incremental horizontal force are also discussed. The last part of the thesis is dedicated to a sensitivity analysis aimed at evaluating the influence of the main geometrical and mechanical parameters on the seismic capacity and failure mechanisms of groin vaults. A non-commercial code implemented in Matlab, based on the upper bound approach of standard limit analysis, was used. The results were finally processed through a multiple linear regression analysis in order to get simplified analytical equations for expedite seismic evaluation of existing groin vaults.